Introduction
Cordocentesis (PUBS) samples fetal blood from the umbilical cord under ultrasound guidance when other tests are insufficient. It can diagnose anemia, infection, chromosomal problems, or bleeding disorders in selected cases.
It is invasive with procedure-specific risks—not routine screening. Maternal–fetal medicine specialists perform it when benefit clearly outweighs risk.
Why this test is done
Cordocentesis (Fetal Blood Sampling) is commonly considered in situations such as:
- Diagnose or monitor fetal anemia (for example Rh isoimmunization)
- Rapid confirmation of chromosomal or genetic problems when indicated
- Evaluate suspected congenital infection
- Provide access for intrauterine transfusion when needed
- Clarify abnormal ultrasound or other fetal test results
How the test is done
- Ultrasound locates the cord; a fine needle obtains blood through the maternal abdomen
- Local anesthesia may be used
- Samples go to the lab; timing varies by tests ordered
- Fetal heart rate is monitored after the procedure
Preparation and precautions
- Follow fasting and medication instructions
- Bring blood type, antibody, and infection screening records
- Report bleeding disorders or anticoagulant use
- Discuss risks, benefits, and alternatives (amniocentesis, CVS, NIPT) beforehand
Understanding results
Your clinician interprets lab or imaging ranges together with your symptoms. Online “normal values” do not always apply to your case.
- Fetal hemoglobin/hematocrit may show anemia
- Karyotype or genetic results may take days to weeks
- Infection PCR or serology is interpreted in clinical context
- Results guide transfusion timing, delivery planning, or other care
Risks or limitations
- Bleeding, fetal bradycardia, or infection
- Rupture of membranes or preterm labor
- Rare fetal loss—risk varies by center and indication
- Maternal–fetal mixing may require anti-D when applicable
After the test
- Rest as instructed; avoid heavy activity briefly
- Call for pain, fever, bleeding, or decreased fetal movement
- Do not miss follow-up ultrasound or monitoring
Frequently asked questions
Is cordocentesis a replacement for amniocentesis?
No. Indications differ—amniocentesis samples amniotic fluid; cordocentesis samples fetal blood.
When is it performed?
Usually after the second trimester at a gestational age chosen by your specialist.
Is it painful?
Needle insertion may cause pressure or pain; local anesthesia and support are provided.
Important caution
This article is general health information. It is not personal medical advice or a prescription.
Your clinician decides whether you need this test, how to prepare, and what the results mean. If you have emergency symptoms, go to hospital without waiting for a lab report.